1. Field of the Invention
The present invention relates to a method for evaluating dispersibility of powder and a method for evaluating concentration of airborne powder especially potent materials, and a method for designing a containment facility for powder using the above methods. More specifically, the present invention relates to a method for evaluating the dispersibility of a powder and a method for evaluating the concentration of airborne powder, in which the dispersibility of the powder is quantitatively evaluated using a trace amount of powder enabling the quantitative design and performance evaluation of a containment facility, and a method for designing a containment facility for the powder using the above methods.
Priority is claimed on Japanese Patent Application No. 2007-143171, filed May 30, 2007, and on Japanese Patent Application No. 2007-211386, filed Aug. 14, 2007, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Conventionally, in the apparatus for measuring powder dispersibility, a method, in which an airborne powder generated in a certain manner is collected on a filter and then chemically quantified, or a method, in which information on the amount of airborne powder is obtained from the laser diffraction data with respect to sample air, has been adopted.
Examples of the apparatus for measuring powder dispersibility which adopts a method to chemically quantify the amount of collected powder include the MI Dustiness Tester developed by Cowherd et al.
In this measuring apparatus, about 100 g of a powder put in a beaker inside a container is dropped to the bottom of the container to disperse the powder (for example, see Cowherd, C. J R, M. A. Grelinger, P. J. Englehart, R. F. Kent, K. F. Wong, “An Apparatus and Methodology for Predicting the Dustiness of Materials”, American Industrial Hygiene Association Journal, 50 (3), 1989, pp. 123-130, and Heitbrink W. A., “Factors Affecting the Heubach and MRI Dustiness Tests”, American Industrial Hygiene Association Journal, 51 (4), 1990, pp. 210-216.).
Further, in the study by Heubach, 10 to 200 g of a powder put in a rotary drum is dispersed by rotating the rotary drum (for example, see Heitbrink W. A., “Factors Affecting the Heubach and MRI Dustiness Tests”, American Industrial Hygiene Association Journal, 51 (4), 1990, pp. 210-216, and Heitbrink W. A., T. C. Cooper, W. F. Todd, D. M. O'Brien, “Dustiness Testers as a means of evaluating the dust exposure potential of powders”, Proceedings of the Technical Program. Annual Powder & Bulk Solids Conference/Exhibition, 1989, pp. 539-549).
Furthermore, in the study by Carlson, a powder is dropped from a hopper called “Laboratory Dust Disperser” and the dropped powder is then introduced into a container for measurement using an air blow device that is set perpendicular to the hopper (for example, refer to Carlson K. H., D. R. Herman, T. F. Markey, R. K. Wolff, M. A. Dorato, “A Comparison of Two Dustiness Evaluation Methods”, American Industrial Hygiene Association Journal, 53 (7), 1992, pp. 448-454).
With the above methods, although the amount of airborne powder can be evaluated in terms of mass concentration, at least a few tens of milligrams of the powder need to be collected in order to directly measure the powder mass. Therefore, with these methods, a large amount of powder sample is required, making it difficult to measure a toxic powder or an expensive powder.
When a chemical analysis is conducted, measurement will be possible if about a few hundred nanograms of a powder can be collected. Hence, it is possible to reduce the amount of powder sample to about 10 g. However, since the chemical determination is required, it is necessary to select different analytical methods (including pretreatment methods and measuring instruments) for each target powder depending on its chemical composition.
For example, when lactose is quantitatively determined, the entire substance collected on a filter is dissolved in about 10 cc of water since this substance is water soluble, and thus it will be possible to determine the substance down to a level of a few hundred nanograms by analyzing this solution down to a level of 10 ppb using high performance liquid chromatography. However, when dealing with water-insoluble powders, the selection of appropriate solvents is also required. In addition, powders need to be collected for a few hours or even longer in order to secure the required amount of samples.
As described so far, sophisticated knowledge of analytical chemistry is required for the powder analysis, and thus easy measurement of the amount of airborne powder has been a challenge. Especially when the sample is a newly developed API (active pharmaceutical ingredients), measurement of the amount of airborne sample will be extremely difficult due to its low availability and high cost, and also for the lack of established analytical methods.
On the other hand, examples of the devices employing laser diffraction for measuring powder concentration include devices known as the Dust View and the STRIKER.
In the Dust View, 30 g of a powder is dropped all at once in a container to disperse the powder (for example, see Hamelmann F., E. Schmidt, “Methods for Characterizing the Dustiness Estimation of Powders”, Chemical Engineering & Technology, 27 (8), 2004, pp. 844-847.).
In the STRIKER, a container known as a cuvette containing powder is patted several times at its bottom by a beating device equipped with a spring to disperse the powder (for example, see Castor W., A. Gray, “Evaluating the dustiness of powders”, Powder Handling & Processing, 2 (2), 1990, pp. 145-148.).
With these methods, information on the number concentration can be obtained rapidly as the powder measurement is performed using a laser. However, information on particle size and density is required for converting the number information to the mass data. Moreover, although the conversion is readily made if the shape of the particles is simply spherical, the actual powder has a complex shape, and thus the conversion has not been easy. Furthermore, since different types of powders have different shapes, comparison between different powders has been even harder.